Spinning of acrylonitrile polymer solutions



United States Patent Ofiice 3,368,015 Patented Feb. 6, 1968 3,368,015 SPINNING OF ACRYLONITRILE POLYMER SOLUTIONS Wilhelm lrion and Werner Saar, Neumunster, Germany, assignors to Phrix-Werke Aktiengesellschaft, Hamburg, Germany No Drawing. Filed July 9, 1963, Ser. No. 293,862 Claims priority, application Germany, July 23, 1962, P 29,884 8 Claims. (Cl. 264-182) The present invention relates to the spinning of acrylonitrile polymer solutions, and more particularly to the production of solutions of polyacrylonitrile and of solutions of copolymers thereof including a high proportion of polyacrylonitrile, and to the spinning of these solutions.

The production at normal temperature of solutions of polyacrylonitrile and copolymers with a high proportion of polyacrylonitrile by dissolution the polymer in aqueous solutions of zinc chloride or mixed salts of zinc chloride and calcium chloride or zinc chloride and sodium chloride, and the wet spinning of such solutions is known.

However, such solutions are very sensitive to coagulation, particularly with water. The precipitation in water proceeds so quickly at the nozzle that the system easily tears upon drawing. In order to be able to spin with acceptable drawing speeds and to be able to form good fibers which necessarily require slow and gentle coagulation, it has been necessary to use salt baths of high concentration, and the more concentrated the salt baths the more mild the action on the dissolved polymers.

For reasons of economy, there is generally used as precipitating bath solutions the same salts as in the spinning solutions. In US. Patent No. 2,790,700, for example, pre cipitating bath concentrations of solutions of zinc chlorides and their mixed salts from 25% and up are claimed.

It is a primary object of the present invention to provide a method of modifying polyacrylonitrile spinning solutions so as to lower the coagulation point thereof and to thereby facilitate spinning of such solutions.

It is another object of the present invention to provide a method of modifying spinning solutions of polyacrylonitrile and copolymers thereof in aqueous solutions of zinc chloride or mixed salts of zinc chloride with other chlorides so as to permit the use of lesser concentrations of the salt in the solution while still holding back coagulation of the solution. As a result, handling of these solutions for spinning purposes and the like is facilitated.

In addition it is another object of the present invention to provide a method of treating such spinning solutions of polyacrylonitrile and copolymers thereof in aqueous zinc chloride solutions so as to improve the properties of the polyacrylonitrile fibers which are spun from such solutions.

It is still another object of the present invention to provide a method of spinning polyacrylonitrile fibers from spinning solutions containing the same, using an intermediate treatment of the solution after the same is formed and before the spinning, whereby spinning is facilitated and better quality fibers are obtained in an easier manner.

It is still another object of the present invention to provide a method of determining how satisfactorily spinning solutions of polyacrylonitrile and copolymers thereof in spinning solutions having the best adaptability for spinning of the fibers can be used.

Other objects and advantages of the present invention will be apparent from a further reading of the specification and of the appended claims.

With the above and other objects in view, the present invention mainly comprises the heating of a spinning solution of polyacrylonitrile or copolymers of polyacrylonitrile ocntaining a high proportion of polyacrylonitrile, the

aqueous zinc chloride solutions can be spun so that only i polymer being dissolved in an aqueous solution of zinc chloride or of mixed salts including zinc chloride, for sev'- eral hours to several days, depending upon the temperature used, and also depending upon the pH of the solution as will be further discussed below, until the tendency of the solution to coagulate has been lowered to such extent that the solution can be easily spun to fibers, and then spinning polyacrylonitrile fibers from the solution.

For purposes of convenience the treatment step of the present invention wherein the spinning solution is subjected to a heating step for a period of time suflicient to reduce the tendency of the solution to coagulate (which will hereinafter be referred to as lowering of the coagulation point of the solution) will be referred to as a ripening process, and reference will also be made to the degree of ripening of the polymers in the salt solutions.

It has been found that the tendency of the spinning solution to coagulate, that is the sensitivity of the dissolved polymer to coagulate, is considerably lowered by subjecting the solution of the polymer in the aqueous salt solution to the ripening process of the invention. Quite surprisingly, as a result of this treatment solutions of the polymers in baths with salt concentrations below 25%, even in Water, can be spun satisfactorily.

Furthermore, and of at least equal importance, it has been found that the modification of the spinning solutions by the so-called ripening process of the present invention results in considerable improvement in the physical properties of the fibers obtained therefrom.

Throughout the rest of the specification and claims of this case reference will be made to the spinning polyacrylonitrile. It is to be understood that this refers not only to homopolymerisates, that is polymerisates formed solely of polyacrylonitrile, but also to copolymers of acrylonitrile with any of the numerous substances with which the same can form copolymers such as acrylic acid, methacrylic acid, methacrylic acid methyl ester, vinyl pyridine, vinyl imidazol, vinyl acetate, etc., in which the percentage of acrylonitrile in the copolymers, is at least of the total. Generally such mixed polymerisates will contain between 85-95% of acrylonitrile and the rest one or more of the above or similar components.

For spinning purposes thepolyacrylonitrile in the solution should generally have a molecular weight of at least 40,000, and usually the molecular weight is not higher than about 120,000. The preferred molecular weight of the polyacrylonitrile polymers for the purposes of the present invention is between 60,000 and 70,000. i

The polyacrylonitrile is dissolved in aqueous zinc chloride solutions, and it is these solutions which are subjected to the method of the present invention. The solutions may contain only zinc chloride as the salt in solution, or it may contain a mixture of zinc chloride with calcium chloride or a mixture of zinc chloride with sodium chloride or a mixture of zinc chloride with magnesium chlo- 3 ride. For purposes of convenience the specification will hereinafter refer to zinc chloride solutions. However, it is to be understood that these solutions include either solutions of zinc chloride alone or mixed salt solutions of the type indicated above.

The preferred concentration of the salt in the zinc chloride solutions of the present invention is between 40 and 65% by weight, and most preferably about 5254% by weight. In the case of mixed salt solutions, a solution containing 60% concentration of the total mixed salt should preferably contain in the case of a mixed salt of ZnCl /CaCl between 35 and 50% of zinc chloride, and most preferably about 40% of zinc chloride which is equal to a ratio of zinc chloride to calcium chloride of 2:1.

In the case of a mixed salt ZnCl /NaCl of 60% total salt concentration the zinc chloride content should preferably be between 40 and 55%, and most preferably about 45% which is equal to a ratio of zinc chloride to sodium chloride of 3:1.

As indicated above, the ripening process of the present invention comprises the heating of the zinc chloride-containing polyacrylonitrile spinning solution for some time to achieve lowering of the coagulation point of the solution. The heating according to the present invention is carried out at a temperature between 35 and 120 C., preferably at a temperature between 50 and 100 C., and most preferably at a temperature between 60 and 80 C., the most preferred temperature being about 70 C. The time of the heating depends upon the particular temperature used.

At the preferred temperature of 50 C. the time of heating will be between four days and seven days and at the preferred temperature of 100 C. the time of heating is between 6 hours and 15 hours. At the lower temperature of 35 C. the heating time is correspondingly increased, while at the higher temperature of 120 C. the heating time is correspondingly reduced At the preferred temperature of 6080 C. the heating time is somewhat in between the times given above.

Although the present invention is not meant to be limited as to any theory of how or why the ripening process of the present invention achieves the results that it does achieve, the following theory is given in the hopes that it will help others in further investigations in this field. It is believed that because of the weakly acid nature of the solvent, the ripening process of the present invention causes changes in the dissolved polymers possibly to result in a more or less mild saponification of the CN- groups of polymers to amide groups, and to a lesser extent possibly also to carboxyl groups.

It is preferred according to the present invention that the salt solution used for dissolving the polyacrylonitrile therein be in the slightly acid range, that is that the same have a pH of somewhat less than 7. Most preferably the pH should be between about 4.0 and 5.5. If the salts in the water do not give the desired pH, then the same can be adjusted to be slightly acid by acidification with a mineral acid, most preferably with hydrochloric acid.

Thus, for example, a solution of polyacrylonitrile of molecular weight of 50,00070,000 in a 60% zinc chloride mixed salt solution (ZnCl /CaCl in mol ratio of 2:1), the solution having a pH value of 5.0, can be spun in water under about the same conditions if prior to the spinning it is either heated for about 15 hours at 90 C., or about 30 hours at 80 C., for about 72 hours at 70 C., or about 120 hours at 60 C. In all cases approximately the same degree of ripening is achieved.

If it is desired to spin a solution under the same circumstances in which the polyacrylonitrile is dissolved in a pure 60% zinc chloride solution (pH 4.2), then the thermal modification should preferably be carried out under milder conditions, for example about 48 hours instead of 72 hours at 70 C.

This indicates that the pH value of the solution also has an effect on the specific conditions to be used for the ripening according to the present invention, However, the specific conditions in any particular case, for any particular solution can easily be determined by pretesting, and in addition, the present invention provides a special method for determining in any case what is herein referred to as the degree of ripening, which special method can in any case indicate the suitability of the polyacrylonitrile solution for spinning.

The method of determining the degree of ripeness of spinning solutions according to the present invention is based on the precipitation of polymers in dilute solutions thereof in concentrated salt solutions, the precipitation being achieved by stirring with water.

The following is a description of the procedure for determining the degree of ripeness of spinning solutions in zinc chloride solutions:

2 g. of the spinning solution are weighed into a small tube, diluted with 10 cc. of the solvent with which the spinning solution has been formed, for example 60% aqueous zinc chloride solution, and homogenized. Then by the slow dropwise addition of water at room temperature under continuous stirring precipitation takes place. At the sudden occurrence of turbidity, which is extremely sharp, the amount of water used in cc. is read, This value may be designated as the ripeness number or the degree of ripening.

Solutions which have not been thermally treated in accordance with the present invention have a ripeness number of between 3.5 and 4.5. Solutions which have been treated thermally for too long a period of time, and which can no longer be used for formation of good quality fibers, have a ripeness number of about 10l2. Between these two values lie the spinning solutions which are most suitable for spinning of good quality fibers in a satisfactory and easily controllable manner. These solutions have ripeness numbers of between 5.8 and 8.0, and most preferably between about 6 and 7. Spinning solutions with ripeness numbers of between 5.5 and 8.0 can be spun in Water to fibers with particularly valuable properties, especially with respect to an unusually high twist strength.

From a ripeness number of 5.5 and higher, fibers spun from such solutions exhibit a peculiar shrinking quality. Thus, such fibers or fiber cables from solution having a ripeness number of 8-9 shrink at temperature above C., for example in water at C. or glycol at C. to a very great extent, in the extreme case to of its original length. However in shrunk condition in the hot medium of the shrinking bath the fiber or fiber cable remains so thermoplastic that it can be stretched to its original length without sticking, and upon cooling remains at the length. However, if it is again introduced into the shrinking bath, it again shrinks to its original shrunk length.

If the heat treatment of the fibers is carried out under tension, for example with the fibers tightly wound on a spool, the shrinking characteristic and the strength and tension properties can be changed, the plastic properties of the fibers under heat however remaining.

In general, copolymers have a greater tendency towards shrinking than the pure polymerisates.

The method of the present invention is in general ap plicable to all types of polyacrylonitrile solutions and all concentrations of such solutions. In general, however, it is preferred to use polyacrylonitrile solutions of between about 7 and 14% concentration, and most preferably of about 10% concentration.

It is possible by the method of the present invention to produce high titer fibers having extremely good physical constants, that is a high strength and tension with excellent elasticity in transverse direction, and with improved ability to take up colors. The titer size can be adjusted by shrinking, which in turn is a result of variation of temperature and length of pretreatment of the spinning solution. The thus obtained fibers are particularly useful for the production of carpets and similar textile materials. The following examples are given to further illustrate the present invention. The scope of the invention is not, however, meant to be limited to the specific details of the examples.

EXAMPLE 1 A pure polyacrylonitrile polymerisate having a molecular weight of 58,000 is worked up into a spinning solution which contains polymer, 54% salt and 36% water by means of a 60% aqueous zinc chloride-calcium chloride solution (2:1). This solution is treated for 3 days in a drying chamber at 70 C., cooled to room temperature, and using the determination method given above is found to have a ripeness number of 6.3.

The solution is spun through a 400 hole nozzle made of tantalum with the holes having a diameter of 0.25 mm. each. Tap water at C. is used as-the precipitation bath, in which the fiber bundle can be very well drawn with a precipitation stretch of 8 cm. and a drawing speed og 3.5 meters per minute. The output volume amounts to 41 cc./min., corresponding to 6.1 g. of polyacrylonitrile per minute.

After passing throughvarious washing baths, of which the first consists of salt solution, the second 10% salt solution and the third and fourth water, the bundle is stretched in boiling water in a ratio of 1:6.6, passed through a drying cylinder heated to 50 C., and finally wound onto a spool with a final drying speed of 24 meters per minute. Its moisture content amounts to 35% P 0.

When dried in air at room temperature without tension the bundle shrinks 2.5%. It consists of smooth, shiny, soft and supple individual fibers having an individual titer of 6.6 with a tension of 22%, and upon introduction into boiling water shrinks an additional 28%. This results in a very good crimping. The individual titer of the thus shrunk fiber amounts to 10.5 denier, the tension 38%.

A portion of thus treated bundle is introduced into a shrinking bath of glycol at 170 C. and maintained in the bath for 1 minute. This results in an additional shrinking of 32%, whereby the bundle becomes yellow in color. The individual titer now amounts to 15.1 denier. The fiber is afterwards as before very well curled and supple and exhibits a tension of 88%.

The properties of the fibers obtained by shrinking in boiling water according to this example are set forth in Table I below. As comparison there is given the corresponding values of fibers of the same polyacrylonitrile in the same salt solution which, however, was not subjected to the prior thermal treatment of the present invention.

TABLE I From thermally From nonthertreated spinning mally treated solution shrinking spinning solution The extremely high Winding strength of the shrunk fibers is noteworthy, this high winding strength meaning that the fibers have a high degree of elasticity in transverse direction, and the fibers are therefore particularly suitable for the production of carpeting and the like.

The cross section of the thus produced fibers have a round form, as do fibers of non-thermally treated spinning solutions, however, in contrast to fibers from non- 6 thermally treated spinning solutions the fibers according to the present invention are finely serrated on the periphery thereof. These fibers of the present invention are more suitable for coloring by dyeing than fibers spun in the normal manner from zinc chloride solutions.

If the fibers are permitted to shrink freely in a shrinking bath (for example water of C.), the same, if quickly taken from the bath, can still in hot condition be stretched to its original length or more. If the thus stretched fibers are again introduced into the shrinking bath, the same shrink to the same extent as before, and this procedure can be repeated indefinitely.

EXAMPLE 2 A copolymer of 94% acrylonitrile and 6% acrylic acidmethyl ester, having a molecular weight of 55,800 is worked up as in Example 1, with a zinc chloride mixed salt solution (ZnCl /CaClin a ratio of 2:1) to a 10% solution and ripened according to the present invention for 3 days at 70 C. until a ripeness number of 6.9. The solution is spun through a 400 hole tantalum nozzle, each hole having a diameter of 0.25 mm., at an output volume of 41 cc./rnin. using a drawing tension of 3.5 meters per minute at the nozzle, the spinning being in water of 15 C. and using a precipitation stretch of 7 cm. After the previously described procedure (hot Water stretching 1:6.6, drying drum 50 C., final draw 24 meters) the resulting fiber has a moisture content of 43% and is wound on spools. The resulting fiber has a good open lustrous appearance, is soft and pliable. The individual fibers have a titer of 6.8, and upon introduction into boiling water shrink 38% and introduction into glycol at C. shrink 79%.

The properties of the shrunk fiber are similar to the fiber of Example 1. The relative winding strength in this case is still higher than in Example 1. The elasticity characteristics of the fibers upon heating is the same as in Example 1.

The fiber shrinks 8% more than that of Example 1, the tension is higher and the strength lower. The values are set forth in Table II below.

The copolymer solution of Example 2 is heat treated for 5 days at 60 C. (instead of for 3 days at 70 C. as in Example 2) thereby obtaining a ripeness number between 6 and 7. The ripeness number actually amounts to 6.1. The spinning conditions are the same as in Example 2 (3.5 meter nozzle draw, stretching 1:6.6, final draw of 24 meters). The wound fibers have a moisture content of 63%, shrink upon drying without tension in air at 4.3%, and is lightly curled and well opened.

In boiling water the fiber shrinks an additional 23.8%. In glycol at 170 C. the fiber shrinks an additional 31.7%, and in both cases the shrinking results in a very high degree of curling or crimping.

As can be seen in comparison with Example 2, the shrinking with a ripeness number 6.1 is less than with the ripeness number of 6.9 (in hot water 28.1% as compared to 38.0%).

The fiber properties are, as shown in Table III below, somewhat changed:

TABLE III Treatment time, Treatment. time, 3 5 days at 60 C. Itipe days at 70 C. Ripeness Number 6.1 ness Number -0.0

A pure polyacrylonitrile polymerisate, as in Example 1, is worked up to a spinning solution. The solution is maintained for 2 days in a drying chamber at 80 C. until a ripeness number of 9.7 is obtained, it is then cooled to room temperature and at a volume output of 32 cc./min. (=48 g. of polymerisate per minute) spun through a 120 hole nozzle made of steel and having as the diameter of the holes 0.45 mm., the spinning being at a drying speed of 6 meters at the nozzle.

- Water at a temperature of C. is suitable as the precipitation bath, the precipitation stretch amounting to 10 cm. After passing through the washing baths, as in Example 1, the fibers are stretched in boiling water in a ratio of 116.6, conducted through a drum heated at 70 C., and wound onto spools with a final drying speed of 38 meters per minute. The moisture content amounts to 81% H O. Upon drying in air without tension the fiber shrinks 1.6%. The fiber is practically uncurled, smooth, fairly lustrous and supple. The individual fibers have an individual titer of 11.4 and shrink in boiling water an additional 72.3%, resulting in a very strong curling or crimping. 0

The individual titer of the thug shrunk fiber now amounts to 41, the tension approximately 60%. If the same fiber is heated for 1 minute in glycol at 170 C. it further shrinks an additional 16.9%, so that the total shrink amounts to 91%. This shrink is obtained if the nonshrunk fiber, without previous shrinking in hot water, is directly immersed in the glycol bath at 170 C. As a result of this treatment the fiber mass becomes intensively yellow colored.

If the fiber piece which has shrunk from 100 cc. to 9 cc. is taken out of the hot shrinking bath and directly stretched, it can be stretched to its original length, without the individual fibers sticking together, and it solidifies upon cooling to this length (approximately 120 cm.). By again introducing the thus stretched fiber into the glycol bath at 170 C. the fiber again shrinks together to a length of 9 cm.

EXAMPLE 5 A pure polyacrylonitrile polymerisate having a molecu- G0 lar weight of 58,000 is brought into an aqueous solution of pure zinc chloride such that the final homogeneous spinning solution contains 10% polymer, 53% zinc chloride and 37% water.

This solution is subjected to a temperature of 70 C. in a heating chamber until a ripeness number of 6.4 is obtained. This condition is obtained in hours.

The solution is cooled to room temperature and then spun through a 400 hole tantalum nozzle having a hole diameter of 0.25 mm. into a precipitation bath which consists of water at about 15 C. The solution is drawn at an output of 36 cc./ min. from the nozzle, and at a precipitation stretch of 4 cc., and drawn from the bath at a speed of 3.5 meters per minute. The fiber bundle is freed of salt in several washing baths and then stretched in 7 boiling water in a ration of 1153. At a drawing speed of 18 meters per minute, the fibers are passed in several windings over a drying drum heated at 50 C. so that the fiber winding on the subsequently placed spool winding arrangement has a moisture content of 33%.

The fiber bundle is shiny, well opened, without sticking, the individual fibers have a titer of 7.6 denier, and it shrinks upon drying in air without tension to an extent of 2%. An additional shrinking of 42% occurs in boiling water, whereby the individual titer increases to 12.6 denier and the fibers obtain a high degree of curling.

As can be seen in Table IV below, the fibers moreover possess a high tension with good tear strength, and unusually high winding strength.

TABLE IV Shrunk in water at Not shrunk 100 C. Individual titer 7.6 12.6 Tear strength dry in km. of own wt. before tear 38.9 25.5 Tension dry in km. before tear 18.7 70.9 Absolute winding strength in km.

before tear 10.0 20.8 Relative winding strength in percent 25.6 81.3

A sample taken from the heating chamber with a ripeness number of 5.9, after 48 hours, spun in the same way gives fibers with considerably less hot water shrinking and does not give as high a tear strength and winding strength eifect as does the above fiber.

The same spinning solution, if not subjected to a thermal treatment according to the present invention, results in fibers which after shrinking in water at 100 C. exhibit the following characteristics:

TABLE v Individual titer 11.7 Tear stength dry in km. of own wt. before tear 18.5 Tension dry in km. before tear 33.3 Absolute winding strength in km. before tear 4.9 Relative winding strength in percent 26.5

EXAMPLE 6 This example illustrates the determination of the ripeness number in accordance with the present invention.

After subjecting the spinning solution of Example 1 to a heat treatment for 3 days at 70 C., 2 g. of the spinning solution are introduced into a small tube. The spinning solution in the tube is diluted with 10 cc. of a 60% solution of zinc chloride-calcium chloride in a ratio of 2: 1. The tube is shaken to form a homogeneous solution.

Water is then slowly added dropwise to the solution in the tube, while constantly agitating, until turbidity occurs. This occurs sharply after 6.3 cc. of water have been added to the tube. Consequently, the ripeness number of this solution is 6.3.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications Without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Method of improving the spinnability of polyacrylonitrile solutions, which comprises subjecting a spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polyacrylonitrile composed of at least by weight of acrylonitrile units, dissolved in an aqueous 9 zinc chloride solution to a heat treatment at a temperature of between about 35 C. and 120 C., and terminating said heat treatment when the addition under stirring of between about 5.5 and 8.5 cc. of water to 2 g. of said spinning solution diluted with cc. of said aqueous zinc chloride solution causes the resulting solution to become turbid; and spinning the thus treated spinning solution.

2. Method of improving the spinnability of polyacrylonitrile solutions, which comprises subjecting a spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polyacrylon'itr-ile composed of at least 85% by weight of acrylonitrile units, dissolved in an aqueous zinc chloride solution, said solution having a pH of between about 4.0 and 5.5, to a heat treatment at a temperature of between about 50 C. and 120 C., and terminating said heat treatment when the addition under stirring of between about 5.5 and 8.5 cc. of water to 2 g. of said spinning solution diluted with 10 cc. of said aqueous zinc chloride solution causes the resulting solution to become turbid; and spinning the thus treated spinning solution.

3. Method of improving the sp'innability of polyacrylonitrile solutions, which comprises subjecting a spinning solution consisting essentially of at least one polymer selected from the group consisting of 'polyacrylonitrile and copolymers of poly-acrylonitrile composed of at least 85% by weight of acrylonitrile units, dissolved in an aqueous solution of a salt selected from the group consisting of zinc chloride, a mixture of zinc chloride and calcium chloride in which the Zinc chloride constitutes at least about 50% by weight of the mixture, a mixture of zinc chloride and magnesium chloride in which the zinc chloride constitutes at least about 50% by weight of the mixture, and a mixture of zinc chloride and sodium chloride in which the zinc chloride constitutes at least 60% by weight of the mixture, said solution being in slightly acidic pH range, to a heat treatment at a temperature of between about 50 C. and 100 C., and terminating said heat treatment when the addition under stirring of between about 5.0 and 8.5 cc. of water to 2 g. of said spinning solution diluted with 10 cc. of said aqueous solution causes the resulting solution to become turbid.

4-. Method of improving the spinnability of polyacrylonitrile solutions, which comprises subjecting a spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polyacrylonitrile composed of at least 85% by weight of acrylonitrile units, dissolved in an aqueous solution of a salt selected from the group consisting of zinc chloride, a mixture of zinc chloride and calcium chloride in which the zinc chloride constitutes at least about 50% by weight of the mixture, a mixture of zinc chloride and magnesium chloride in which the zinc chloride constitutes at least about 50% by weight of the mixture, and a mixture of zinc chloride and sodium chloride in which the zinc chloride constitutes at least 60% by weight of the mixture, said solution containing between about 40 to 65% by weight of said salt and being in slightly acidic pH range, to a heat treatment at a temperature of between about 50 C. and 100 C., and terminating said heat treatment when the addition under stirring of between about 5.0 and 8.5 cc. of water to 2 t of said spinning solution diluted with 10 cc. of said aqueous solution causes the resulting solution to become turbid; and spinning the thus treated spinning solution.

5. Method of improving the spinnability of polyacrylonitrile solutions, which comprises subjecting an approximately 714% by weight spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polyacrylonitrile composed of at least 85% by weight of acrylonitrile units, dissolved in an aqueous zinc chloride solution, said solution containing between about 40 and 65% by weight of Zinc chloride and being in slightly id acidic pH range, to a heat treatment at a temperature of between about 50 C. and 100 C., and terminating said heat treatment when the addition under stirring of between about 5.5 and 8.5 cc. of water to 2 g. of said spinning solution diluted with 10 cc. of said aqueous zinc chloride solution causes the resulting solution to become turbid; and spinning the thus treated spinning solution.

6. Method of improving the sp-innability of polyacrylonitrile solutions, which comprises subjecting an approximately 714% by weight spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polya-crylonitrile composed of at least by weight of acrylonitrile units, and having a molecular weight of be tween about 40,000 and 120,000 dis-solved in an aqueous solution of a salt selected from the group consisting of zinc chloride, a mixture of zinc chloride and calcium chloride in which the Zinc chloride constitutes at least about 50% by weight of the mixture, a mixture of zinc chloride and magnesium chloride in which the zinc chloride constitutes at least about 50% by weight of the mixture, and a mixture of zinc chloride and sodium chloride in which the zinc chloride constitutes at. least 60% by weight of the mixture, said solution containing between about 4-0 and 65% by weight of said salt and being in slightly acid pH range, to a heat treatment at a temperature of between about 50 C. and C., and terminat ing said heat treatment when the addition under stirring of between about 5.5 and 8.5 cc. of water to 2 g. of said spinning solution diluted with 100 cc. of said aqueous solution causes the resulting solution to become turbid; and spinning the thus treated spinning solution.

7. Method of improving the spinnability of polyacrylonitrile solutions, which comprises subjecting a spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polyacrylonitrile composed of at least 85% by weight of acrylonitrile units, dissolved in an aqueous zinc chloride solution to a heat treatment at a temperature of between about 35 C. and C. until said solution [has a ripeness number of between 5.5 and 8.5, the ripeness number being the number of cubic centimeters of water required to cloud 2 grams of said spinning solution diluted with 10 cubic centimeters of said aqueous zinc chloride solution; and spinning the thus treated spinning solution in water at approximately room temperature.

8. Method of improving the spinnability of polyacrylonitrile solutions, which comprises subjecting an approximately 744% by weight spinning solution consisting essentially of at least one polymer selected from the group consisting of polyacrylonitrile and copolymers of polyacrylonitrile composed of at least 85% by weight of acrylonitrile units and 'having a molecular weight of between about 40,000 and 120,000 dissolved in an aqueous solution of a salt selected from the group consisting of Zinc chloride, a mixture of Zinc chloride and calcium chloride in which the zinc chloride constitutes at least about 50% by weight of the mixture, a mixture of zinc chloride and magnesium chloride in which the zinc chloride constitutes at least about 50% by weight of the mixture, and a mixture of zinc chloride and sodium chloride in which the zinc chloride constitutes at least 60% by weight of the mixture, said solution containing between about 40 and 65% by weight of said salt and being in slightly acidic pH range, to a heat treatment at a temperature of between about 50 C. and 100 C., and terminating said heat treatment when the addition under stirring of between about 5.5 and 8.5 cc. of water to 2 g. of said spinning solution diluted with 10 cc. of said aqueous solution causes the resulting solution to become turbid, and spinning the thus treated spinning solution in Water containing less than about 25% by weight of Zinc chloride.

(ReEercnces on following page) References (Iied UNITED STATES PATENTS Stanton et a1. 260-29.6 Stanton et a1. 264-1 82 Stanton et a1. 26029.5 Taniyama et a1 264-182 Lowes 264- 182 X Nakajima et a1. 260-2916 Murdock et a1. 264-182X 12 FOREIGN PATENTS 1,009,760 11/1965 GreatBritain.

5 ALEXANDER H. BRODMERKEL,

Primary Examiner. 

1. METHOD OF IMPROVING THE SPINNABILITY OF POLYACRYLONITRILE SOLUTIONS, WHICH COMPRISES SUBJECTING A SPINNING SOLUTION CONSISTING ESSENTIALLY OF AT LEAST ONE POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYACRYLONITRILE AND COPOLYMERS OF POLYACRYLONITRILE COMPOSED OF AT LEAST 85% BY WEIGHT OF ACRYLONITRILE UNITS, DISSOLVED IN AN AQUEOUS ZINC CHLORIDE SOLUTION TO A HEAT TREATMENT AT A TEMPERATURE OF BETWEEN ABOUT 35*C. AND 120*C., AND TERMINATING SAID HEAT TREATMENT WHEN THE ADDITION UNDER STIRRING OF BETWEEN ABOUT 5.5 AND 8.5 CC. OF WATER TO 2 G. OF SAID SPINNING SOLUTION DILUTED WITH 10 CC. OF SAID AQUEOUS ZINC CHLORIDE SOLUTION CAUSES THE RESULTING SOLUTION TO BECOME TURBID; AND SPINNING THE THUS TREATED SPINNING SOLUTION. 